A pearl is formed as a result of a defense mechanism against foreign irritants by mollusks. For many species, following the intrusion of the foreign irritant, the mantle tissue of the mollusk secretes aragonite or a mixture of aragonite and calcite (both crystalline forms of calcium carbonate) and conchiolin (a horn-like protein) to coat the irritant. The combination of aragonite and conchiolin is called nacre, or mother-of-pearl. The secretion is repeated many times and the irritant is then covered by several layers of nacre, forming a pearl. Accordingly, pearls produced by the nacre secretion process are called nacreous pearls.
In addition, there are also non-nacreous pearls (sometimes referred to as “calcareous concretions”), that are porcellaneous (i.e., have a low-luster, ceramic-like surface). Many pearls of this type are non-attractive and valueless but among them, pearls in species such as conch (Strombus gigas), and various scallop species are still of interest.
A conch pearl is produced by the conch family Strombidae. Conch pearls display various colors that range from white to brown with a wide variation in yellow, pink and orange hues (Fritsh and Misiorowski, 1987; Federman and Bari, 2007). For example, the queen conch, Strombus gigas, naturally produces valuable pearls that can exhibit an attractive pink color (Acosta-Salmon and Davis, 2007). The conch pearl frequently exhibits a characteristic “flame” structure or pattern on its surface. This flame effect, also called “chatoyancy,” is caused by fibrous prismatic crystals perpendicularly aligned to the surface of the pearl (Federman and Bari, 2007). Unfortunately, natural conch pearl products are lacking around the world because of their rarity. Their desirability warrants the need for cultured conch pearls.
There are two main techniques for the production of cultured pearls. One is the technique used in marine pearl oysters, developed and refined by the Japanese in the early 1900s, in which a nucleus (or bead) and a piece of mantle tissue from a donor pearl oyster are implanted into the gonad of a recipient pearl oyster, a process known as “grafting,” “beading” or “seeding” (Acosta-Salmón et al., 2004; CIBJO, 2006). Generally only one or two nuclei can be implanted at one time, depending on the pearl oyster species and the grafting technician.
The second technique is used in freshwater mussels. This technique has many variations and has been continuously developing (Fiske and Shepherd, 2007). Briefly, it involves grafting pieces of mantle tissue from a donor mussel into the mantle of a recipient mussel (Dan and Ruobo, 2003; Fiske and Shepherd, 2007); this process is frequently called “tissue nucleation,” although this term is incorrect because the mantle tissue is never the nucleus in a non-beaded cultured pearl. Grafting success rates for cultured pearl production vary widely. For example, mortality of freshwater mussels at the first pearl harvest is around 90% (Fiske and Shepherd, 2007). On the other hand, after grafting the blacklip pearl oyster, Pinctada margaritifera, 10% of the oysters died and a further 20% rejected the nucleus (Ellis and Haws, 1999). Mortalities between 2 and 24% and bead rejections between 9 and 16% were observed in P. margaritifera subjected to different post grafting treatments (Norton et al., 2000).
U.S. Pat. No. 3,871,333 discloses a method of producing cultured pearls in abalones by perforating a hole through the shell of the abalone, depositing a nucleus bead on the reproductive organ of the abalone through the hole, covering the hole, and raising the treated abalone until pearls are formed.
EP Patent Application No. 1,084,615 discloses a nucleus for producing blister or mabé pearls in mollusks. The nucleus is generally bell-shaped with a dome and a peripheral edge portion. The surface of the peripheral edge portion and some or all of the dome includes one or more steps which start at, or adjacent to, the outer edge. The steps assist by providing a key for the deposition of nacre. The nucleus may be secured to the shell of the mollusk in a variety of ways.
U.S. Pat. No. 5,347,951 discloses a process for nucleating pearls in shell-bearing mollusks by forming an opening in the shell of a host mollusk in a region covering a soft tissue, providing a pearl nucleus having a first portion around which nacre forms and a second portion securely connected to the first portion and having a region larger than the size of the opening, and manually inserting the nucleus through the opening to an implanted position.
PCT Application No. PCT/NZ98/00167 discloses a nucleus for the production of half or mabe pearls in mollusks. The nucleus comprises a first portion having an external surface adapted to define the shape of the half or mabe pearl to be produced and a second portion that defines a bridge between the first portion and the shell of the host mollusk. The half or mabe pearls so produced have a substantially even cross section of nacre formed over the nucleus, and a generally reduced time is required for the formation of the pearl.
Published U.S. Patent Application No. 2004/0112086 discloses a method of producing pearls including inserting a nucleus into a mollusk able to produce a pearl, incubating the nucleus within the mollusk, and removing a portion of the nacre coating, thereby exposing a portion of the nucleus.
The techniques described in the above disclosures all have certain drawbacks, such as the necessity for perforating a hole in the shell at a location covering a soft tissue, which is often difficult and causes high mortality. Thus, although queen conch aquaculture methods are well established (Davis and Shawl, 2005), attempts to develop techniques to produce cultured pearls in this species have been unsuccessful to date (Federman and Bari, 2007).
There is a considerable need for a method of commercially culturing conch (family Strombidae) pearls and pearls from other gastropods (e.g., families Haliotididae and Volutidae). The subject invention provides methods for culturing non-beaded and beaded conch pearls with success rates (retention and survival) comparable with those achieved in commercial oyster pearl operations.